Controller and LED driving circuit with protection function

Abstract

A controller with protection function, for controlling a transistor having a control terminal, a first terminal coupled to a load, a second terminal, is disclosed. The controller comprises a judgment unit and a current control unit. The judgment unit is coupled to the transistor and generates a current reducing signal when a potential of the first terminal of the transistor or a voltage difference between the first terminal and the second terminal of the transistor is higher than a preset value. The current control unit is coupled to the control terminal of the transistor for substantially stabilizing the current flowing through the transistor at a preset current value, and reduces the current flowing from the preset current value when receiving the current reducing signal.

What is claimed is: 
     
       1. A controller with protection function, used to control a transistor having a control terminal, a first terminal coupled to a load and a second terminal, comprising:
 a judgment unit, coupled to the transistor and generating a current reducing signal when a potential of the first terminal of the transistor or the voltage difference between the first terminal and the second terminal of the transistor is higher than a first preset value; and 
 a current control unit, coupled to the control terminal of the transistor to control a current flowing through the transistor to substantially be a preset current value and reducing the current when receiving the current reducing signal, 
 wherein the second terminal of the transistor is coupled to a current detecting unit which generates a current detecting signal according to an amount of a current flowing through the current detecting unit and controls the current flowing through the transistor according to the current detecting signal, the current detecting unit comprises a first current detecting resistance and a second current detecting resistance and the current control unit comprises a select switch, and an end of the select switch is coupled to the second terminal of the transistor and the other end thereof is coupled to the first current detecting resistance or the second current detecting resistance according to the current reducing signal. 
 
     
     
       2. The controller with protection function according to  claim 1 , wherein the judgment unit comprises a first voltage divider element coupled to the first terminal of the transistor and a comparison element coupled to the first voltage divider element, and the comparison element generates the current reducing signal according to the potential of the first terminal of the transistor and a first compared reference voltage. 
     
     
       3. The controller with protection function according to  claim 1 , wherein the judgment unit further generates a protection signal when the potential of the first terminal of the transistor or the voltage difference between the first terminal and the second terminal of the transistor is higher than a second preset value, in which the second preset value is higher than the first preset value. 
     
     
       4. A controller with protection function, used to control a transistor having a control terminal, a first terminal coupled to a load and a second terminal, comprising:
 a judgment unit, coupled to the transistor and generating a current reducing signal when a potential of the first terminal of the transistor or the voltage difference between the first terminal and the second terminal of the transistor is higher than a first preset value; and 
 a current control unit, coupled to the control terminal of the transistor to control a current flowing through the transistor to substantially be a preset current value and reducing the current when receiving the current reducing signal, the current control unit further comprises a reference voltage generating unit which is used to generate a reference voltage, the current control unit adjusts the amount of the current flowing through the transistor according to the level of the reference voltage and the reference voltage generating unit reduces a level of the reference voltage when receiving the current reducing signal, 
 wherein the reference voltage generating unit comprises a second voltage divider element, a switch element, and a voltage adjustment element, and the second voltage divider element receives a base voltage to generate a reference voltage, in which a terminal of the switch element is coupled to the second voltage divider element and another terminal thereof is coupled or de-coupled to the voltage adjustment element according to the current reducing signal to adjust the level of the reference voltage. 
 
     
     
       5. The controller with protection function according to  claim 4 , wherein the judgment unit further generates a protection signal when the potential of the first terminal of the transistor or the voltage difference between the first terminal and the second terminal of the transistor is higher than a second preset value, in which the second preset value is higher than the first preset value. 
     
     
       6. A controller with protection function, used to control a transistor having a control terminal, a first terminal coupled to a load and a second terminal, comprising:
 a judgment unit, coupled to the transistor and generating a current reducing signal when a potential of the first terminal of the transistor or the voltage difference between the first terminal and the second terminal of the transistor is higher than a first preset value; and 
 a current control unit, coupled to the control terminal of the transistor to control a current flowing through the transistor to substantially be a preset current value and reducing the current when receiving the current reducing signal, 
 wherein the second terminal of the transistor is coupled to a current detecting unit which generates a current detecting signal according to an amount of a current flowing through the current detecting unit and controls the current flowing through the transistor according to the current detecting signal, the current control unit further comprises a signal add unit which is coupled to the current detecting unit and increases the level of the current detecting signal at a preset value in response to the current reducing signal.